The present invention relates to a method and apparatus for detecting pneumatic pressure in the intake passage downstream of the throttle valve of an internal combustion engine.
In an internal combustion engine, the relative pneumatic pressure (negative pneumatic pressure) in the intake manifold must be detected in order to execute ignition timing control or exhaust gas recirculation (EGR) control (in the case of using an EGR value controlled by the atmospheric pressure and the negative pneumatic pressure in the intake manifold). For this purpose, the relative pneumatic pressure in the intake manifold is detected by a relative pneumatic pressure sensor. In the internal combustion engine of the fuel injection type in which the amount of fuel injection is controlled depending upon the running speed of the engine and the absolute pneumatic pressure in the intake manifold, however, it is an essential requirement that the absolute pneumatic pressure in the intake manifold be detected. The engine of this type, therefore, must be equipped with both a sensor for detecting relative pneumatic pressure in the intake manifold and a sensor for detecting absolute pneumatic pressure in the intake manifold. Otherwise, the engine must be provided with either one of the two types of sensors, and the detected value must be utilized for finding the other value. The former method makes it possible to maintain good control precision in the control operations but requires two sensors and, hence, necessitates increasing the manufacturing cost. According to the latter method, on the other hand, no compensation is effected when the atmospheric pressure is changed and, hence, control precision is greatly decreased. Consequently, it is difficult in the case of the latter method to cope with the stringent regulations placed on exhaust gases in recent years.